The eddy currents and coil energization generate heat in the eddy current coupling. A cooling medium, such as air or water, is supplied to the coupling housing to carry off this heat.
In liquid cooled couplings, the coolant is usually introduced at the top of the housing and applied directly to the rotating parts, for example, the exterior of the inductor drum. The coolant splashes on the rotating parts to remove their heat and is collected in a drain at the bottom of the housing.
It will be appreciated that the presence of the coolant within the housing raises the possibility of moisture of the field coil. If such contamination occurs, electrical breakdown and premature failure of the coil can result.
The centrifugal action of the rotating parts tends to lessen contamination when the rotor and inductor drum are rotating by flinging the coolant away from the interiorly mounted coil. However, significant contamination can result from coolant dripping off the parts when they are stationary.
Such contamination can be resisted by encapsulating the coil in an impervious potting compound and/or hermetically sealing the coil in an enclosure, such as an annular copper can. However, these steps add to the manufacturing costs, reduce electrical efficiency, and are still subject to failure from thermal or other stresses.